An volcano is a mountain from which lava and hot gasses erupt ... Lava from Nyiragongo volcano, inundates Goma, Congo. Goma airport closed by lava flow ...
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September 21, 2005
An volcano is a mountain from which lava and hot gasses erupt
Low silica rocks (e.g. basalts) very fluid
High silica rocks (e.g. rhyolites) very viscous
Gasses under pressure cause explosions
Gasses are poisonous
The Volcanic Explosivity Index, or VEI, was proposed in 1982 as a way to describe the relative size or magnitude of explosive volcanic eruptions. It is a 0-to-8 index of increasing explosivity. Each increase in number represents an increase around a factor of ten. The VEI uses several factors to assign a number, including volume of erupted pyroclastic material (for example, ashfall, pyroclastic flows, and other ejecta), height of eruption column, duration in hours, and qualitative descriptive terms.
About 1500 volcanoes worldwide
Most eruptions last 10 - 1000 days
Less than 20% over within 72 hours
Median is 7 weeks (1176 hours)
Cumulative number of eruptions
With eruptive volumes equal to or
Greater than the given amount
Eruptions obey Gutenberg-Richter
Statistics: lots of small ones, just
a few big ones.
The graph at the left are for
Explosive eruptions in Kamchatka
During the last 10,000 years
strong mantle upwelling to ‘fill in hole’, so lots of basaltic magmatism (almost all of which is under water)
Thicker crust suppresses mantle melting somewhat, but can add volatiles
dewatering of subducted lithosphere (string at 100-150 km depth) suppresses the melting point of mantle rock to produce basaltic magma
Strong thickening of crust can cause once-shallow, water-rich crustal rocks to be buried. They can heat up and melt to produce granitic melts
rising mantle plumes lead to melting that
produces basaltic magmas and Hawaii-type volcanic islands
Thick lithosphere leads to greater degree of chemical variability, broader range of lava types.
Case of Goma, Congo
a city with a population 500,000, located near Rwanda border, on shore of Lake Kivu, affected by lava from Nyiragongo Volcano
Jan 17, 2002, 45 people died, 50,000 displaced. Eruptions with deaths in 1977, too.
Burns from coming in contact with lava or hot rock, or from buildings set afire.
High concentrations of poison gases that are being emitted from the lava.
Destruction of infrastructure that supplies vital services (water, etc)
Mt. Rainier, Washington State
Lots of water locked up in that
summit glacier …
Note glacier at summit, valley that channels water
Was innundated by several meters
Being buried alive in thick, gooey mud
Hot gasses and dust “burp” out of the volcano’s summit and cascade downhill at speeds of 50-100 mph.
town of St. Pierre
350 meters high, was a rock spire
that was pushed up out
Of the crater of Mt. Pele in 1902 as
new lava rose beneath the volcano.
Explosive volcanism at volcanic island caused a tsunami in nearby water
Local tsunamis, like the one following the Krakatau eruption, are the most common. But ocean-crossing tsunamis are possible. The ca. 1625 BCE eruption of the Agean island of Thera is an example.
Note location of volcano: island in center of narrow straight between two populated land masses, Java and Sumatra
extremely large explosion
collapse of the volcanic edifice
30 meter high tsunami hits coast of
Java and Sumatra, killing
165 villages totally destroyed
Inland by 1883 tsunami
Being crushed by floating debris
Ash falls over broad area, like snow
weight of ash collapses house
ash makes road impassible
ash-covered grass poisonous
to livestock (e.g. Iceland, 1783)
larger chucks of rock (=bombs) also fall
Aerosols (particularly sulfate) injected high is the atmosphere
reflect sunlight back to space, resulting in net cooling of the
Unseasonably cold temperatures case crop failures
June 9-10, 1816: On the 9th, frost was reported as far south as Worcester, Massachusetts and on the 10th to East Windsor, Connecticut.
July 6, 1816: Temperatures in the 40’s F range were reported in Connecticut at both Hartford and New Haven. Robbins in East Windsor noted temperatures almost cold enough for a frost.
Extremely large VEI=6
eruption in 1815.
May have been the
Largest in 10,000 years
Perhaps 90,000 people
Died worldwide, from
Very local hazards
Explosion induced tsunami
Chemical pollution by ash